1. Technical Field
The present invention relates in general to lapping workpieces, and in particular to improving the precision of a lapping process for magnetic transducers. Still more particularly, the present invention relates to a precisely controlling lapping of a workpiece having an element that is recessed in or protruding from the lapped surface of the air bearing surfaces of magnetic transducers.
2. Description of the Prior Art
Magnetic recording is employed for large memory capacity requirements in high speed data processing systems. For example, in magnetic disc drive systems, data is read from and written to magnetic recording media utilizing magnetic transducers commonly referred to as magnetic heads. Typically, one or more magnetic recording discs are mounted on a spindle such that the disc can rotate to permit the magnetic head mounted on a moveable arm in position closely adjacent to the disc surface to read or write information thereon.
During operation of the disc drive system, an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disc where the head electromagnetically reads or writes data. Usually the head is integrally mounted in a carrier or support referred to as a “slider.” A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disc drive system. The slider is aerodynamically shaped to slide over moving air and therefore to maintain a uniform distance from the surface of the rotating disc thereby preventing the head from undesirably contacting the disc.
Typically, a slider is formed with two parallel rails having a recessed area between the rails and with each rail having a ramp at one end. The surface of each rail that glides over the disc surface during operation is known as the air bearing surface. Large numbers of sliders are fabricated from a single wafer having rows of the magnetic transducers deposited simultaneously on the wafer surface using semiconductor-type process methods. After deposition of the heads is complete, single-row bars 11 (see FIG. 1) are sliced from the wafer, each bar comprising a row of units which can be further processed into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated into sliders having one or more magnetic transducers on their end faces.
The slider head is typically an inductive electromagnetic device including magnetic pole pieces which read the data from or write the data onto the recording media surface. In other applications the magnetic head may include a magneto resistive read element for separately reading the recorded data with the inductive heads serving only to write the data. In either application, the various elements terminate on the air earing surface and function to electromagnetically interact with the data contained on the magnetic recording disc. In order to achieve maximum efficiency from the magnetic heads, the sensing elements must have precision dimensional relationships to each other as well as the application of the slider air bearing surface to the magnetic recording disc. During manufacturing, it is most critical to grind or lap these elements to very close tolerances of desired thickness in order to achieve the unimpaired functionality required of sliders.
Conventional lapping processes utilize either oscillatory or rotary motion of the workpiece across either a rotating or oscillating lapping plate 13 (FIG. 1) to provide a random motion of the workpiece 11 over lapping plate 13 and randomize plate imperfections across the head surface in the course of lapping. During the lapping process, the motion 15 of abrasive particles 17 (FIGS. 2 and 3) carried on the surface of the lapping plate 13 is typically transverse to or across the magnetic head elements 19 exposed at the slider air bearing surface 21. In magnetic head applications, the electrically active components 19 exposed at the air bearing surface are made of relatively softer, ductile materials. These electrically active components during lapping can scratch and smear into the other components causing electrical shorts and degraded head performance. The prior art lapping processes cause different materials exposed at the slider air bearing surface 21 to lap to different depths (FIG. 4), resulting in recession or protrusion of the critical head elements 19 relative to the air bearing surface 21. As a result, poor head performance because of increase space in between the critical elements and the recording disc can occur.
Rotating lapping plates having horizontal lapping surfaces in which abrasive particles such as diamond fragments are embedded have been used for lapping and polishing purposes in the high precision lapping of magnetic transducing heads. Generally in these lapping processes, an abrasive slurry utilizing a liquid carrier containing diamond fragments or other abrasive particles is applied to the lapping surface as the lapping plate is rotated relative to the slider or sliders maintained against the lapping surface. Common practice is to periodically refurbish the lapping plate with a lapping abrasion to produce a surface texture suitable for the embedding and retention of the appropriate size of diamond abrasive being used with the lapping process. One of several problems experienced is that the surface is susceptible to rapid change in smoothness as it is used to lap a workpiece during lapping. A change in smoothness effects the hydrodynamic bearing film provided by the liquid component of the abrasive slurry creating a hydroplaning effect which raises the workpiece from the lapping surface to diminish the abrasion action of the particles and substantially increases abrasion time required.
The general idea of interrupting the lapping surface, for example, by forming grooves in the lapping plate is known in the art. Further, material has been used in the troughs so that unspent abrasive liquid is maintained adjacent to the working surface of the lapping plate while spent abrasive fluid is centrifugally removed beyond the lap plate peripheral. In other applications, the grooves are formed between working surface area in which an abrasive such as diamond particles are embedded in a metallic coat.
Problems exist with grooved plates such as excessive width and/or depth of the grooves to allow abrasive particles to lose their effectiveness due to lack of contact with a workpiece. Grooves that are too wide provide surface discontinuity too severe for small work pieces. Forming such grooves is costly and time consuming. Even if the grooves can be sized properly. Substantial segments of the lapping surface remain ungrooved, or alternatively a prohibitively large number of grooves are required. Surface uniformity on a micropore scale suitable for lapping smaller pieces has been achieved only with extreme care. Refurbishment of such sensitive grooving on a lapping surface required renewal of the precision grooves can be time consuming and expensive. Therefore it can be seen that there is a need for precise conditioning and texturing of the plate surfaces of lapping plates in order to maintain surface flatness, waviness, and microprofile of the grooves in the lapping (polishing) plate. It can also be seen that there is a need for machine conditioning of lapping plates with such conditioning and texturing so as to extend the life of lapping plates. In addition, there is a need for enhanced quality of plate surfaces to yield better quality, scratch-free air bearing surfaces or other surfaces which require soft material lapping having a uniformly textured lapping surface amenable to repeat refurbishment.